I did my first show as a live sound engineer last night, as a favor to a friend and was hoping for some advice on what I *should* have done, for next time.... ;)

The main issue was that the show was for 9 different groups of learner guitarists, from 3 to 8 in each group. So at one point we had 8 acoustic guitars, plus bass and elec all going into the same desk, with whatever guitar leads I could find stretched across the stage like spaghetti. It was chaos, but all very good humored.

The sound was ok, but very muddy, so after some reading this morning I think some of the guitars were impedance mis-matched, as they were piezo pickups going directly into the desk. Is this right?

How should I have done this from a cable and connection perspective? Should I use a stage box running to directly to the desk? Or multiple DI boxes? Or one big DI box? Or a sub mixer on stage?

What would be best practice for bringing order to this chaos (apart from employing a professional)?

I'd doubt many beginners would have guitars with just piezo elements and no on-board pre-amp. If they had volume knobs and EQ controls, then they would have had pre-amps and would be fine to bring directly in to the desk (though for long runs, plugging into a local DI box would have helped reduce any noise pickup on long unbalanced leads.

There are also quite a few guitars with no volume controls but still have a basic pre-amp connected to the endpin jack. Again, these are the same as above.

Then you may get a few guitars that only have an internal piezo pickup which connects directly to an endpin jack. These need to be fed to an external preamp which has an input impedance of around 10 megohms. This high impedance is needed to get a flat EQ from the pickup. Lower than that and although the signal is louder, it's not a nice sound at all. 10 meg impedances aren't common, so you'd need to use a pre-amp dedicated for such devices. Even a standard active DI box wouldn't provide a high enough impedance for a good sound.

So I wouldn't expected the PA to have provided acoustic pre-amps for the guitars. If the guitarist wants you to use their electric signal, then it's down to them to supply a suitable pre-amped signal for you. If they can't, then you'd have to mic them up as best you can.

For next time, you really need to find out what each type of pickup/preamp each guitarist has on their guitar, which should be provided by the guitar tutor(s) prior to the show.

And unless you want to go and buy some piezo pre-amps, or have the tutors provide them, then I'd have a few mics ready for those ones with just a plain piezo output. An SM57 pointed at the 12th fret provides a reasonable acoustic guitar sound and is fairly feedback resistant.

I provide the rig for an annual (every November) multi-band fundraiser show.It's always an interesting night.I usually get a program with each band's instrumentation list a week prior to the show. About three years ago a band showed up with 7 (SEVEN) guitars besides bass/ etc.. four of which did not bring amps.The four dudes come up to me and ask "Where do I plug in?" I only had two channels of DI available...I told them to figure it out...

I'd go passive DI's. I use three Horizon Stereoline two channel DI's almost exclusively. I do have an active DI (LR Braggs) which I have only used once in the past five years...The passive DI's that I use also have ground-lift switches that can help when chasing a hum/buzz.

Secondly, I agree with the comments above. The guitars will almost certainly have active pre-amps and could go straight into the mixer, but passive DIs will be way better.The main reason for the muddiness though is nothing to do with the technology per se, it's just the sound of eight :o beginner guitarists all playing much the same thing at the same time! So for next time, here's what I would do - assuming you don't have time to individually set up each group with a leisurely sound check and it's all going to be a bit rushed ;)The bass & electric are constant, possibly the tutors? Get a setup with those two instruments plus one well-played acoustic. Take out almost everything below 100Hz from the electric and acoustic, roll off the bass above 3Khz . Adjust eq to taste to get a reasonable mix, if in doubt scoop a bit more out of the electric. Agree in advance with the tutors who are the better players in each group, and that they will sit in the same seats and therefore on the same desk channels. Set the eq up on those channels as per your reference guitar.For the rest of the acoustic guitars cut everything below 100Hz, and take out mud around 200 Hz. They will sound awful on their own, but that's not the point.Adjust faders so that you have the bulk of the melody from the well played guitars, and the rest adding to the impression of volume, but not to mud. Tweak as required.

I'm sure there are FOH gurus out there throwing up their hands/lunch in horror, but it's a starter for 10 to clear out the mud. If the sound is too thin you can always put some back.

The other thing I would do, which will be easier with DI boxes and long mic leads, is to run all the cables cleanly together, either under chairs if they are seated or in a line with the music stands if they are standing. I've found repeatedly that a clean stage helps give the musicians confidence you know what you're doing, and (particularly beginners) play better.

trouserpressface wrote:So at one point we had 8 acoustic guitars, plus bass and elec all going into the same desk, with whatever guitar leads I could find stretched across the stage like spaghetti.

As others have said, in the ideal world you should get a source list in advance of the gig so you can plan your equipment requirements and stage box plugging etc, and won't get caught out when 8 guitarists turn up at the same time looking for somewhere to plug in!

'Spaghetti' across the stage is never a good idea -- you really don't want people tripping over cables. This is partly because it's a great way to break the cables, but it could also break any connected instruments, or worse, break someone's neck -- and you really don't want to have to fill in all those public liability insurance forms! That is a very painful road to go down...

But absolutely do make sure you have appropriate PL insurance in place because accidents can and will happen regardless of how careful you are, and when they do they will come looking for big compensation payouts.... Being a member of some organisations (like the MU) can provide free PL cover, or you can get it via specialist brokers.

I would usually recommend that you run your cable routes along the front or back of the stage area where possible, and certainly never across the main paths on/off the stage. Run the cables in straight lines and tape them down where practical, too.

Often it can be advantageous to run one or more 8-way multicore tails from the main stagebox across to the other side or rear of the stage, just to reduce the number and length of individual mic cables running across the stage. Coil any spare cable neatly at the source end, not the stagebox end, so you can move source positions easily if necessary.

Where instruments need to go straight into DI boxes, place those by the musicians' chairs, music stands, etc, as has already been said. If they need to go near the amps, place them adjacent, but beware stray magnetic fields from the amp main transformer inducing hum into the DI box's audio transformer.

Individual DI boxes are usually more flexible, but if you have a lot of sources in one area (eg a Wakeman-style keyboard rig) it can be worth hiring in a multichannel DI box. If the DI box has a ground lift function, start with the ground connected and only engage the ground lift if you find a ground-loop hum problem. With guitars plugged straight into the DI and no onward route to an amp, it is very unlikely that you'll need the ground lift at all.

If an instrument or source is already actively amplified (eg, active guitars, guitars with built-in preamps, keyboards, drum machines, DJ mixers etc etc) then a passive DI box is fine as the source won't be worried about the load impedance. For normal (passive) electric guitars with magnetic pickups, active DI boxes are generally better as they usually have a higher input impedance (1M Ohm or so) which will maintain the guitar's tone better... but they will need powering via battery or phantom power. Piezo pickups typically need a very high input impedance (10M Ohms or more) which us why most are used with dedicated preamps.

The sound was ok, but very muddy, so after some reading this morning I think some of the guitars were impedance mis-matched, as they were piezo pickups going directly into the desk. Is this right?

As someone else has already said, the mud was more likely just because of the number of guitars and unskilled players. With acoustic guitars it's usually necessary to roll off a considerable amount of low end to get that mud under control!

However, as mentioned above, piezo pickups often need a very high input impedance to give the best tone, and neither the mic nor line inputs of a normal desk will get anywhere close. However, if the guitars had onboard preamps you'd have been fine.

WRT di boxes, as Hugh says, passives are not suitable for raw piezo pickups. Orchid Electronics sell an active DI for only £25 (including postage within the UK). I have three and they work pretty well for acoustic guitars. They do require phantom power as there is no battery option.

As most of those acoustics will have on-board pre-amps with EQ controls (normally bass middle and treble), it may be worthwhile getting the tutors checking that before they go on stage that they are either set flat or with a small degree of mid-scoop. At least you'll then avoid excessive bass boost or random peaky settings from the guitarists who never normally play amplified but may play around with their faders.

Those damn tone controls on acoustic guitars are hated by most right thinking sound guys....... I work with a singer guitarist who refuses to sing loud at the soundcheck (he's saving his voice for the gig!) and "likes to leave a bit in hand" on his guitar volume...... Drives me mad......

Thanks everyone for your great advice and suggestions - I've learnt more in this one thread than in days of trawling the web!

I've agreed to do another one of these shows in 8 weeks, so I'm going to make sure I'm prepared this time, with proper stage cabling, a few active DI boxes and a list of exactly what the guitars are that are going to be on stage so I know how to treat each one.

And the suggestions about how to 'manage' the sound of the players during the performance are really good, some wise heads here.

Been there and done it, we had an 8 way rack DI but, TBH, separate DI boxes are much more versatile and 8 x Orchid Micro DIs costs a few quid less than the one linked to. Ask yourself, how many times am I going to have 8 guitars close enough together to run into one box? I doubt we ever used more than 3 or 4 in that rack at any one time (and still need a couple of separate DIs elsewhere on the stage.

Sam Spoons wrote:Been there and done it, we had an 8 way rack DI but, TBH, separate DI boxes are much more versatile and 8 x Orchid Micro DIs costs a few quid less than the one linked to. Ask yourself, how many times am I going to have 8 guitars close enough together to run into one box? I doubt we ever used more than 3 or 4 in that rack at any one time (and still need a couple of separate DIs elsewhere on the stage.

Good point, and if you attach them with Velcro they can be easily removed for another part of the stage...